1. Field of the Invention
The present invention relates to a controller for controlling the position and/or speed of a driven body in a working machinery such as tool machinery.
2. Description of the Related Art
In working machinery such as tool machinery, machining is carried out by moving a tool relative to a work which is to be machined. In order to control the machining position or speed, the driven body (work, table with a work mounted thereon, or tool) is driven with a servo motor, and usually position feedback, speed feedback, and current feedback control is conducted to control the position or speed of the driven body.
Machining position, speed and machining torque are controlled by such feedback control of position, speed, and current, but when the speed and acceleration of the driven body change rapidly, vibrations sometime occur in the driven body due to such rapid changes. In particular, when positioning of the driven body to the machining position in working machinery is conducted by rapid feed, vibrations occur due to a rapid change in speed when the driven body is stopped, and if the machining operation such as cutting is started immediately after the positioning, the driven body (work, table, tool) is subjected to the next operation such as machining in a vibrating state, the next operation cannot be implemented with high accuracy, and if the next operation is cutting, then precision machining cannot be conducted. Furthermore, when the next operation after the positioning operation is a tool replacement operation, then the tool replacement cannot be implemented correctly if the driven body was caused to vibrate in the positioning operation.
Accordingly, when a transition is made from a positioning operation such as fast feed operation to a machining operation such as cutting, the next operation such as cutting is started after waiting for a preset waiting time after the positioning has been completed.
Furthermore, in a known configuration (see Japanese Patent Application Laid-open No. H6-91482), an acceleration sensor for detecting the acceleration of a driven body is provided, the signal from the acceleration sensor is deducted from the current command outputted by the speed feedback control, the current command of the current feedback control is corrected, and vibrations of the driven body are suppressed.
With the conventional method, in which when the next operation after the positioning operation of the driven body, such as fast feed, is a machining operation such as cutting or a tool replacement operation, a transition to the next operation of cutting or tool replacement is made after the vibrations calmed down and a stable state was assumed, the waiting time is difficult to set. If a long waiting time is set, the entire machining time increases. Conversely, if a short waiting time is set, the next operation of cutting or tool replacement is started, while the driven body (work, table, tool, etc.) still vibrates, and the desired machining accuracy or correct tool replacement cannot be attained. The optimum waiting time is, therefore, difficult to set.
When the speed is changed rapidly in the course of machining operation such as cutting, there is a risk of vibrations occurring in the driven body and decreasing the machining accuracy.